The present invention relates to oil gels and associated methods of use and preparation. More particularly, the present invention relates to gelled invert emulsion compositions and their associated methods of use and preparation.
Oil gels often are suitable for use in subterranean applications. Using oil gels as opposed to aqueous-based systems may result in such advantages as improved hole stability, especially in shale formations; thinner filter cakes than achieved with aqueous-based systems; desirable lubrication of the drilling string and downhole tools; and effective penetration of salt beds without sloughing or enlargement of the hole. Other benefits are known to those skilled in the art.
Despite the many benefits of utilizing oil gels, they also may have disadvantages. Generally speaking, the use of oil gels may have high initial operating costs. These costs may be significant, depending on the depth of the hole to be drilled. However, often the higher costs can be justified if the oil gel composition prevents the caving in or hole enlargement, which can greatly increase drilling time and costs. Also, although the use of gelled oil compositions may be preferred in some instances, the practical ability to use gelled oil compositions in certain subterranean applications may be hindered because of insufficient density for well control in some cases. For instance, in a gravel packing operation, a gelled oil composition may not have sufficient density to overcome the pore pressures in the subterranean formation. This can lead to inflow of reservoir fluids and/or well bore stability problems. In most drilling operations, solids are used to increase the density of drilling fluids if desired; however, in completion operations, solids-free completion fluids are preferred to minimize potential formation damage. Conventional solids-free completion fluids, however, generally do not have sufficient properties to provide optimal fluids for such operations.
Invert emulsions are types of oil-based fluids that may be used in subterranean applications. Invert emulsions comprise a continuous phase that comprises an oleaginous fluid, and a discontinuous phase that comprises a fluid that is at least partially immiscible in the oleaginous fluid. Invert emulsions that do not have a viscosified continuous phase tend to exhibit similar advantages and disadvantages as do oil gels. Invert emulsions tend to have desirable suspension properties for particulates like drill cuttings. As such, they can easily be weighted if desired. Also, it is well known to reverse invert emulsions to regular emulsions (i.e., those that have an aqueous-based continuous phase and an oleaginous discontinuous phase) using certain conditions such as pH or protonating the surfactant so as to reverse the affinity of the surfactant for the continuous and discontinuous phases. For example, if a residual amount of an invert emulsion remains in a well bore, that portion may be reversed to a regular emulsion to clean out the emulsion from the well bore.